1. Field of the Invention
The present invention is broadly concerned with an apparatus and method for testing the stickiness of a sample, i.e. the adhesive force necessary to separate a probe from a sample. More particularly, the invention concerns an apparatus and method whereby a sample is restrained against a supporting surface during engagement and disengagement by the probe, during which the stickiness of the sample is measured. Restraint of the sample insures that the appropriate adhesive force is measured, and eliminates the possibility that the force required to separate the sample from the support surface is being erroneously measured, as opposed to force required to separate the probe from the sample.
2. Description of the Prior Art
The measurement of adhesive properties of various materials has long been considered by the industrial and scientific communities. Testing equipment is readily available which includes a base supporting a sample, together with a probe which can be lowered and compressed against the surface of the sample, and subsequently withdrawn. During the withdrawal or disengagement of the probe from the sample, the adhesive properties, i.e., the force required to separate the probe from the sample, are measured.
More recently, researchers have endeavored to measure the adhesive properties of food samples, such as pasta products of various shapes including elongated spaghetti products. The stickiness of pastas is one factor in determining a product consistency, inasmuch as the stickiness may affect not only the tendency of the pasta pieces to cling together, but also the organoleptic qualities of the product such as taste and texture. The stickiness of cooked pasta products may also be considered as an important indication of the quality of the wheat midlings or flours used in manufacture of the product.
Past efforts to accurately measure the stickiness of pasta products have met with only limited success. In 1978, Voisey et al. described a stickiness test for cooked spaghetti in "Measuring the Texture of Cooked Spaghetti. 2. Exploratory Work on Instrumental Assessment of Stickiness and Its Relationship to Microstructure", reported in the Canadian Institute of Food Science Technology Journal Vol. 11, No. 4. The test involved placing strands of cooked spaghetti on a lower serrated plate having 90.degree. V-grooves, compressing the strands with a flat upper plate, and then pulling the flat plate away from the strands at a constant rate while measuring the disengagement force with a load cell. In 1983, Dexter et al. published an article in Cereal Chemistry entitled, "Grain Research Laboratory Compression Tester: Instrumental Measurement of Cooked Spaghetti Stickiness". This article reports the use of a Grain Research Laboratory compression tester with a plunger which was moved into and out of engagement with the many spaghetti strands positioned side by side, and used an aluminum retainer plate with an opening for providing plunger to sample access.
A prime difficulty with these prior techniques is that a measurement is taken at one fixed time after cooking, even though surface stickiness changes unpredictably with time. A second difficulty with these methods is due to measurement of the wrong force. When a sample such as cooked pasta is placed upon a support surface and engaged by a probe, lifting of the probe may cause the pasta to separate from the support surface before the probe itself becomes disengaged from the pasta. When this occurs, the force being measured is not a valid measurement of adhesiveness. This is particularly troublesome if pasta separates from the support surface and pasta/probe disengagement occurs on a random or unpredictable basis. This may occur especially when strands of cooked spaghetti or noodles are placed side by side so that water is trapped between and under the strands. A third difficulty is that the former methods rely on a probe with but one type of surface. A probe with multiple types of surfaces and with adjustable surface area would allow the magnification of differences in stickiness. Finally, the old methods are slow and cumbersome with respect to sample preparation and measurement if the operator wishes to make repeated measurements on a sample. Rapid measurement on a single strand of noodle or pasta would permit one to observe changes in stickiness as they occur under ambient room conditions.